Forming processes are used to make large and/or structural glass fiber reinforced composite (GFRC) parts. Such processes include RIM (Reactive Injection Molding), SRIM (Structural Reactive Injection Molding), RTM (Resin Transfer Molding), VARTM (Vacuum Assisted Resin Transfer Molding), SMC (Sheet Molding Compound), BMC (Bulk Molding Compound), spray-up forming, filament winding, LFI (Long Fiber Injection molding) and pultrusion.
In the injection molding process, chopped glass fibers and pellets of a thermoplastic polymeric resin are fed into an extruder to mix the two together at elevated temperature. Substantial working and maceration is important and sometimes necessary to wet out the glass fibers at the elevated temperature due to the high viscosity, and as a result the glass fibers are shortened significantly. The resultant mixture is formed into a molding material that is supplied to a press or injection molding system to be formed with very expensive tooling into GFRC parts. During the extrusion process using single or twin-screw machines, the resin is heated and melted and the fibers are dispersed throughout the molten resin to form a fiber/resin mixture. Next, the fiber/resin mixture may be degassed, cooled, and formed into pellets or slugs. The dry fiber strand/resin dispersion pellets are then fed to a moulding machine and formed into moulded composite articles that have a substantially homogeneous dispersion of glass fiber strands throughout the composite article. Alternatively, in the process using continuous filaments, fiberglass filaments are mixed with the molten resin in an extruder with the screw geometry designed to mix the matrix with fibers without causing significant damage to the fibers. The resultant extruded mixtures are then compression molded to form long-fiber reinforced thermoplastic parts having superior mechanical properties due to the nature of the orientation and the longer length of the fibers. Because of these difficulties, the use of thermoplastics to make vehicle parts was limited.
With the newly proposed challenging CAFÉ gas mileage standards being introduced and growing needs for lighter weight parts in aircraft, there is a greater need for lighter weight parts that thermoplastic fiber reinforced composite (TPFRC) could satisfy. The thermoplastic polymers or copolymers can be recycled by melting and reclaiming, and ground thermoplastic TPFRC can be used in thermoplastic forming processes including injection molding, extrusion, etc. Thus, there is a large need for TPFRC parts using thermoset processes including RIM, SRIM, RTM, VARTM, reactive compounding, reactive injection molding including LFI, SMC, BMC, spray-up hand lay-up etc. if ways could be found to polymerize and form the thermoplastic polymers, copolymers and homopolymers in situ surrounding the fiber reinforcements in a mold.
Low viscosity caprolactam monomers, one containing an activator and another mixture containing a caprolactam monomer and a catalyst may be cast by mixing the two very low viscosity mixtures together prior to casting. However, this mixture often should be kept to less than about 100° C. to prevent rapid polymerization. Following casting, the cast mixture is heated in the mold to cause anionic polymerization of the monomer to produce a polyamide. However, this method is not practical for most vehicle and large parts and many other current thermoset parts because of the relatively low temperature limitation and the time delays that are caused in the forming and polymerizing cycle. If TPFRC is to replace metals or thermoset fiber reinforced composites (TSFRC) substantially in the automotive industry and elsewhere, economical method(s) need to be found that will produce such automotive parts of equal or superior performance at competitive costs with metal and TSFRC parts now in use. This is achieved with the methods described herein.